1981681 has 16 divisors (see below), whose sum is σ = 2298240. Its totient is φ = 1693440.

The previous prime is 1981669. The next prime is 1981687. The reversal of 1981681 is 1861891.

It is a cyclic number.

It is not a de Polignac number, because 1981681 - 2⁵ = 1981649 is a prime.

It is a super-2 number, since 2×1981681² = 7854119171522, which contains 22 as substring.

Its product of digits (3456) is a multiple of the sum of its prime divisors (216).

1981681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (1981687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17481 + ... + 17593.

It is an arithmetic number, because the mean of its divisors is an integer number (143640).

2^1981681 is an apocalyptic number.

It is an amenable number.

1981681 is a deficient number, since it is larger than the sum of its proper divisors (316559).

1981681 is a wasteful number, since it uses less digits than its factorization.

1981681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 216.

The product of its digits is 3456, while the sum is 34.

The square root of 1981681 is about 1407.7219185620. The cubic root of 1981681 is about 125.6062496045.

It can be divided in two parts, 1981 and 681, that added together give a palindrome (2662).

The spelling of 1981681 in words is "one million, nine hundred eighty-one thousand, six hundred eighty-one".